Device and Method for Reducing Contact Resistance of a Metal

ABSTRACT

A structure for an integrated circuit with reduced contact resistance is disclosed. The structure includes a substrate, a cap layer deposited on the substrate, a dielectric layer deposited on the cap layer, and a trench embedded in the dielectric layer. The trench includes a TaN layer deposited on a side wall of the trench wherein the TaN layer has a greater concentration of nitrogen than tantalum, a Ta layer deposited on the TaN layer, and a Cu deposited on the Ta layer. The structure further includes a via integrated into the trench at bottom of the filled trench. In an embodiment, both the TaN layer and the Ta layer are formed with physical vapor deposition (PVD) wherein the TaN layer is formed with plasma sputtering a Ta target with an N 2  flow at least 20 sccm. The structure offers low contact resistance (Rc) and tight Rc distribution.

PRIORITY DATA

This claims priority to U.S. Provisional Patent Application Ser. No.61/677,862 filed on Jul. 31, 2012, entitled “A Method of ReducingContact Resistance of a Metal”, the entire disclosure of which isincorporated herein by reference. This is also a continuation-in-part ofU.S. Ser. No. 13/601,223 filed Aug. 31, 2012, the entire disclosure ofwhich is also incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs and, for these advances to be realized,similar developments in IC processing and manufacturing are needed.

For example, as the critical dimension (CD) of devices are scaled down,any variations in the CD may become more relevant, including resultingvariations in the contact resistance (Rc) of a metal structure in an ICdevice. Accordingly, what is needed is a method for further scaling downof the IC device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with accompanying figures. It is emphasized that,in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposeonly. In fact, the dimension of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a cross sectional view of a device according to one or moreembodiments of the present disclosure.

FIG. 2 is a flow chart of a method of fabricating a device forimplementing one or more embodiments of the present disclosure.

FIGS. 3-14 are cross sectional views of forming a device forimplementing one or more embodiments of the present disclosure.

FIG. 15 is an example of a contact resistance improvement for thedevices of FIG. 1 and FIGS. 3-14.

FIG. 16 provides graphs of different element ratios for the devices ofFIG. 1 and FIGS. 3-14.

FIG. 17 is an X-ray diffraction (XRD) analysis of two TaN compounds forthe devices of FIG. 1 and FIGS. 3-14.

FIG. 18 is a cross sectional view of a device according to one or moreembodiments of the present disclosure.

FIG. 19 is an X-ray diffraction (XRD) analysis of TaN/Ta compounds forthe devices of FIG. 18, in accordance with some embodiments.

FIG. 20 shows graphs of sheet resistance of the devices of FIG. 14 andFIG. 18, in accordance with some embodiments.

FIGS. 21 and 22 shows graphs of contact resistance of the devices ofFIG. 14 and FIG. 18, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

For the sake of comparison, the following disclosure describes threedifferent devices. A first device 100 is described with reference toFIG. 1, and represents a method and device that utilizes physical vapordeposition (PVD) of materials such as tantalum (Ta) and tantalum nitride(TaN) for the deposition of barrier layers inside one or more trenches.A second device 300 is described with reference to FIGS. 2-14, andrepresents a method and device that utilizes different depositiontechniques, such as PVD, atomic layer deposition (ALD), and/or chemicalvapor deposition (CVD) for the deposition of barrier layers inside oneor more trenches. A third device 600 is described with reference to FIG.18, and represents a method and device that utilizes physical vapordeposition (PVD) of materials such as tantalum (Ta) and tantalum nitride(TaN) for the deposition of barrier layers inside one or more trenches.The differences among them will be discussed where appropriate.

Referring to FIG. 1, the device 100 includes a substrate 102, a firstcap layer 104 deposited on the substrate 102, a first dielectric layer106 deposited on the first cap layer 104, a first trench 108 embeddedinto the first dielectric layer 106, a second cap layer 114 depositedover the first trench 108 and the first dielectric layer 106, a seconddielectric layer 116 deposited on the second cap layer 114, a via 118formed on the first trench 108 and buried in the second dielectric layer116, a second trench 124 formed on the via 118 and buried in the seconddielectric layer 116.

The first trench 108 is embedded into the first dielectric layer 106.The first trench 108 includes a first trench metal barrier layer 110deposited on bottom and side walls of the first trench 108 and a firsttrench metal 112 filled into the first trench 108 over the first trenchmetal barrier layer 110. For the sake of reference, a trench metal isalso referred to as a metal and a trench metal barrier layer is alsoreferred to as a metal barrier layer.

The first trench metal barrier layer 110, the via metal barrier layer120, and the second trench barrier metal layer 126 include a PVD TaNlayer and a PVD Ta layer. A contact resistance (Rc) of the first trenchmetal 112 or the second trench metal 128 using the PVD TaN and PVD Ta asa metal barrier layer depends on a critical dimension (CD) of the firsttrench metal 112 and/or the second trench metal 128. The contactresistance (Rc) increases with the CD of the corresponding trench metal.Accordingly, a variation of a contact resistance (Rc) of a trench metalin the IC may significantly impact the performance of the IC.

FIGS. 2-14 describe the second device 300 that provides a lower Rc thanthe first device 100 of FIG. 1, with little or no impact on metal lineresistivity and back end of line (BEOL) reliability.

Referring to FIG. 2, a method 200 of forming the device 300 isillustrated for implementing one or more embodiments of the presentdisclosure. FIGS. 3-14 are cross sectional views of the second device300 formed using the method 200.

The method 200 begins at step 202 by forming a stack of layers on asubstrate 302 as shown in FIG. 3. Step 202 includes depositing a firstcap layer 304 on the substrate 302, depositing a first dielectric layer306 on the cap layer 304, and depositing a hard mask layer 308 on thefirst dielectric layer 306.

In the present embodiments, the substrate 302 includes a wafer with orwithout one or more conductive or non-conductive thin films. The waferis a semiconductor substrate including silicon (in other words, asilicon wafer). Alternatively or additionally, the wafer may includeanother elementary semiconductor, such as germanium; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,GaInP, and/or GaInAsP. In yet another alternative, the wafer may be asemiconductor-on-insulator (SOI). The conductive and non-conductive thinfilms may comprise an insulator or a conductive material. For example,the conductive material comprises a metal such as aluminum (Al), copper(Cu), tungsten (W), nickel (Ni), titanium (Ti), gold (Au), and platinum(Pt) and, thereof an alloy of the metals. The insulator material mayinclude silicon oxide and silicon nitride.

The substrate 302 may include various doped features, such as n-typesource/drain, p-type source/drain, n-type wells, and/or p-type wells,formed by ion implantation or diffusion. The substrate 302 may alsoinclude various isolation features, such as shallow trench isolation(STI), formed by a process, such as a process including etching to formvarious trenches and then depositing to fill the trench with adielectric material. The substrate 302 further includes a gate and acontact hole formed in a front end of line (FEOL) for fabricating asemiconductor IC device.

In some embodiments, the first cap layer 304 includes silicon nitride(Si_(x)N_(y)). The first cap layer 304 is used to prevent metal (e.g.copper) diffusion. The first dielectric layer 306 includes a dielectricmaterial, which may be organic or inorganic. In the present embodiment,the dielectric material includes an organic silicone gel (OSG) with adielectric constant k that ranges from about 2.6 to about 2.65. The lowk dielectric material OSG is formed by a chemical reaction betweenprecursors, such as diethoxy methyl silane (DEMS), and a porogen, suchas α-Terpinene (ATRP) under oxygen (O₂) plasma following by anultraviolet (UV) cure. The first dielectric layer 306 may includesilicon (Si), carbon (C), oxygen (O2), and hydrogen (H). The first hardmask layer 308 includes materials such as silicon nitride (Si_(x)N_(y))or a metal hard mask such as Ti or TiN. Other suitable materials arepossible for the first cap layer 304, the first dielectric layer 306,and the first hard mask layer 308.

The method 200 proceeds to step 206 by forming a first photo resistpattern 310. As shown in FIG. 4, the first photo resist pattern 310 isformed on top of the first hard mask layer 308 deposited on the firstdielectric layer 306. Step 206 includes depositing a first photo resistfilm on the first hard mask layer 308, for example, by a spin-on coatingprocess. In the present disclosure, a photo resist film is also referredto as a resist film. The first photo resist film may include a positivetone resist or a negative tone resist. The first photo resist film mayalso include a single photo resist film or a multiple layer photo resistfilms. Step 206 may include performing a dehydration process beforedepositing the first photo resist film on the hard mask layer 308, whichcan enhance an adhesion of a photo resist film to the hard mask layer308. The dehydration process may include a high temperature baking for aduration of time, or applying a chemical such as hexamethyldisilizane(HMDS) to the hard mask layer 308. Step 206 also includes applying abottom anti-reflection coating (BARC) process to improve profile of aphoto resist pattern. Step 206 includes using a soft bake (SB) processto increase a mechanical strength of the photo resist film.

Step 206 further includes exposing the first photo resist film depositedon the mask layer 308 using a lithography exposing tool. The lithographyexposing tool includes an ultraviolet (UV) light, a deep ultraviolet(DUV) light, an extreme ultraviolet (EUV), or a X-ray light tool. Thelithography exposing tool also includes a charged particle tool, such asan electron beam writer. Step 206 may also include using a mask, such asa binary mask or a phase shift mask (PSM). The phase shift mask may bean alternative phase shift mask (alt. PSM) or an attenuated phase shiftmask (att. PSM). In the present disclosure, a mask is also referred toas a photomask or a reticle.

Step 206 also includes developing the exposed first photo resist filmusing a developer, such as tetramethylammonium hydroxide (TMAH). It ispossible to use an organic solvent as a developer. Step 206 alsoincludes a post exposure bake (PEB), a post develop bake (PDB), or both.Step 206 also includes a rinsing process to remove any developingresidue.

The method 200 proceeds to step 208 by forming a first trench 312 asshown in FIG. 5. Step 208 includes removing a portion of the hard masklayer 308 not covered the first photo resist pattern 310 by using anetching process. Step 208 also includes using a cleaning process tostrip the first photo resist pattern 310 and remove any etching residue.Step 208 further includes forming the first trench 312 using an etchingprocess. The first trench 312 penetrates the first dielectric layer 306and the first cap layer 304 to reach a contact area of the substrate302, such as a gate, a source, a drain, or a capacitor embedded into thesubstrate 302.

The method 200 proceeds to step 210 by filling the first trench 312using conductive material. Step 210 includes depositing a metal barrieron bottom and side walls of the first trench 312. In the presentembodiments, the metal barrier includes multiple layers, formed usingmore than one deposition process. Step 210 includes depositing a firstbarrier layer 314 on the bottom and the side walls of the first trench312 as shown in FIG. 6 using atomic layer deposition (ALD) process orchemical vapor deposition (CVD). Step 210 also includes depositing asecond barrier layer 316 on the first barrier layer 314 using adeposition process, such as a PVD process. In one embodiment, the secondbarrier layer 316 includes only a PVD Ta layer without a PVD TaN layer.In another embodiment, the second barrier layer 316 includes a PVD Talayer with a PVD TaN layer. Both of these embodiments include PVD Ta,but the PVD TaN is optional. It is understood that it is possible to addmore barrier layers. It is noted that a TaN layer formed by an ALDprocess is referred to as ALD TaN, a TaN layer formed by a CVD processis referred to as CVD TaN, a Ta layer formed by a PVD process isreferred as PVD Ta, and so forth. It is further noted that PVD TaN isdifferent from ALD TaN or CVD TaN, as discussed below.

Step 210 further includes filling the first trench 312 with a firsttrench metal 318, such as copper (Cu), as shown in FIG. 6 using adeposition process, such as an electroplating process. In oneembodiment, step 210 may also include depositing a seed layer.

The method 200 proceeds to step 212 by performing a chemical mechanicalpolishing (CMP) process. Step 212 includes removing the first trenchmetal 318, the second barrier layer 316, and the first barrier layer 314outside the first trench 312 as shown in FIGS. 6-7. Step 212 alsoincludes removing the first hard mask layer 308 using an etchingprocess. Step 212 further includes using a pad and slurry for polishing.Step 212 also includes using a scrub cleaning process. As shown in FIG.7, the first trench metal 318 is embedded in the first dielectric layer306.

The method 200 proceeds to step 214 by depositing a second stack oflayers on the first trench metal 318 embedded in the first dielectriclayer 306 as shown in FIG. 8. Step 214 includes depositing a second caplayer 320 on the first trench metal 318 embedded in the first dielectriclayer 306, depositing a second dielectric layer 322 on the second caplayer 320 deposited on the first trench metal 318, and depositing asecond hard mask layer 324 on the second dielectric layer 322 depositedon the second cap layer 320.

As shown in FIG. 8, in the present embodiment, the second cap layer 320includes silicon nitride (Si_(x)N_(y)). The second cap layer 320 is usedto prevent metal (e.g. copper) diffusion between metal layers. Thesecond dielectric layer 322 may include organic or inorganic dielectricmaterial. In the present embodiment, the material includes organicsilicone gel (OSG) with a dielectric constant k ranging from about 2.6to about 2.65. The low k dielectric OSG material is formed by a chemicalreaction between a precursor, such as diethoxy methyl silane (DEMS), anda porogen, such as α-Terpinene (ATRP) under oxygen (O₂) plasma followingby an ultraviolet (UV) cure. The second dielectric layer 322 may includesilicon (Si), carbon (C), oxygen (O₂), and/or hydrogen (H). The seconddielectric layer 322 may be the same or similar to the first dielectriclayer 306. The second hard mask layer 324 includes materials such assilicon nitride (Si_(x)N_(y)) or a metal hard mark like Ti or TiN. Othersuitable materials are possible for the second cap layer 320, the seconddielectric layer 322, and the second hard mask layer 324.

The method 200 proceeds to step 216 by forming a second photo resistpattern 326 as shown in FIG. 9. The second photo resist pattern 326 isformed on top of the second hard mask layer 324 deposited on the seconddielectric layer 322. Step 216 is similar or the same as step 206 whenforming the first photo resist pattern 310 with reference to FIG. 4.

The method 200 proceeds to step 218 by forming a trench 328 as shown inFIG. 10. Step 218 includes removing a portion of the second hard masklayer 324 not covered by the second photo resist pattern 326 using anetching process. Step 218 also includes etching into the seconddielectric layer 322 as shown in FIG. 10. Step 218 further includesusing a cleaning process to strip the second photo resist pattern 326and remove an etching residue.

The method 200 proceeds to step 220 by forming a third photo resistpattern 330 as shown in FIG. 11. The third photo resist pattern 330 isformed on top of the trench 328 and the second hard mask layer 324. Step220 is similar or the same as step 206 when forming the first photoresist pattern 310 with reference to FIG. 4.

The method 200 proceeds to step 222 by forming a via 332 and a secondtrench 334 as shown in FIG. 12. Step 222 includes etching through thesecond dielectric layer 322 and the second cap layer 320 to reach thefirst trench metal 318 by utilizing the third photo resist pattern 330and an etching process. Step 222 also includes stripping the third photoresist pattern 330 using a cleaning process. Step 222 further includesetching the second dielectric layer 322 by utilizing the hard mask layer324 using an etching process.

The method 200 proceeds to step 224 by filling the via 332 and thesecond trench 334 as shown in FIG. 13. Step 224 includes depositing athird barrier layer 336 on bottom and side wall of the via 332 andsecond trench 334 using ALD or CVD. In the present embodiment, the thirdbarrier layer 336 contacts the first trench metal 318. Step 224 alsoincludes depositing a fourth barrier layer 338 on the third barrierlayer 336 using a deposition process, such as PVD. Step 224 furtherincludes depositing a second trench metal 340 on the fourth trenchbarrier layer 338 and filling up the via 332 and the second trench 334using a deposition process, such as an electroplating process. In oneembodiment, step 224 may also include depositing a seed layer of thesecond trench metal.

In the present embodiment, the third barrier layer 336 includes a TaNlayer deposited on the bottom and the side walls of the via 332 and thesecond trench 334 using an ALD process or a CVD process (ALD TaN or CVDTaN). In one embodiment, the fourth barrier layer 338 includes only PVDTa, without PVD TaN. In another embodiment, the fourth barrier layer 338includes PVD Ta with PVD TaN. Continuing with the present embodiments,the second trench metal 340 includes a copper (Cu) formed by using anelectroplating process. The second trench metal 340 may include othermetal or metal alloy.

The method 200 proceeds to step 226 by performing a chemical mechanicalpolishing (CMP) process. Step 226 includes removing the third barrierlayer 336, the fourth barrier layer 338, and the second trench metal 340outside the second trench 332 as shown in FIGS. 13-14. Step 226 includesusing a pad and slurry for polishing. Step 226 also includes using ascrub cleaning process. Step 226 further includes removing the secondhard mask layer 324 using an etching process. Additional steps can beprovided before, during, and after the method 200, and some stepsdescribed can be replaced, eliminated, or moved around for additionalembodiments of the method 200. In the presented embodiments, more trenchmetal layers can be formed by using the method 200.

As shown in FIG. 14, the device 300 fabricated by the method 200includes the substrate 302, the first cap layer 304 deposited on thesubstrate 302, the first dielectric layer 306 deposited on the first caplayer 304, the first trench 312 embedded into the first cap layer 304and the first dielectric layer 306, the second cap layer 320 depositedon the first dielectric layer 306, the second dielectric layer 322deposited on the second cap layer 320, the via 332 integrated on top ofthe first trench 312 and embedded into the second cap layer 320 and thesecond dielectric layer 322, and the second trench 334 integrated on topof the via 332 and embedded into the second dialect layer 322. However,other configurations of the device are possible.

As shown in FIG. 14, the first trench 312 includes a first barrier layer314 deposited on the bottom and the side walls of the first trench 312,the second barrier layer 316 deposited on the first barrier layer 314,and the first trench metal 318 deposited on the second barrier layer 316while filling up the first trench 312. The via 332 includes a thirdbarrier layer 336 deposited on the top of the first trench metal 318 andthe side walls of the via 332, the fourth barrier layer 338 deposited onthe third barrier layer 336, and the second trench metal 340 depositedon the fourth barrier layer 338 while filling up the via 332. The secondtrench 334 includes a third barrier layer 336 deposited on the side wallof the second trench 334, the fourth barrier layer 338 deposited on thethird barrier layer 336, and the second trench metal 318 deposited onthe fourth barrier layer 338 while filling up the second trench 334. Thevia 332 is integrated with the second trench 334. The third barrierlayer 336 and the fourth barrier layer 338 are shared by both the via332 and the second trench 334. Both the via 332 and the second trench334 are filled with the second trench metal 340.

FIG. 15 is a graph 400 that compares the Rc of the device 100 (FIG. 1),identified with the group 402, with the Rc of the device 300 (FIGS.2-14), identified with the group 404. The group 402 includes Rc databetween a first trench metal M1 and a second trench metal M2 with acritical dimension (CD) changing of the M1 and the M2 while the M1 andM2 are deposited on a PVD Ta/TaN. The group 404 includes Rc data betweena first trench metal M1 and a second trench metal M2 with a CD changingof the M1 and the M2 while the M1 and M2 are deposited on an ALD TaN/PVDTa.

The Rc data in group 404 is lower than the Rc data in group 402 atdifferent M1/M2 CDs, with only one exception for M1/M2 at 0.05 μm inwhich they are about the same. As shown in the figure, the Rc in group402 changes from about 6 to about 14Ω, while the RC in group 404 changesfrom about 6 to about 11Ω. It is noted that variations of the Rc data inthe group 404 are smaller than variations of the Rc data in the group402 at different M1/M2 CD locations. It is further noted that the slopeof the Rc change in the group 404 is shallower than a slope of the RCchange in the group 402. Therefore, performance of an IC device isimproved by using device 300, as compared to device 100.

Referring to FIGS. 16 and 17, differences between ALD TaN or CVD TaN, ascompared to PVD TaN, can be shown in different ways. FIG. 16 provides agraph 500 that corresponds to the device 100 (FIG. 1), and a graph 510that corresponds to the device 300 (FIG. 2-14). The graph 510 shows aN/Ta ratio of an ALD TaN to be about 2.3 to 2.6, a N/Ta ratio of a PVDTaN to be about 0.3 to 0.6, and a N/Ta ratio of an ALD TaN/PVD Ta or anALD Ta/PVD TaN/Ta to be about 0.6 to 1.0. The carbon (C) content in aPVD TaN/Ta (graph 500) is lower than about 0.2%, and the C content in anALD TaN/PVD Ta or an ALD TaN/PVD TaN/Ta (graph 510) is about 0.2 to 1%.

Referring to FIG. 17, an x-ray diffraction (XRD) analysis comparing thedevices 100 and 300. A line 520 corresponds to the device 300, and aline 530 corresponds to the device 100. The lines 520, 530 are similar,except in the areas specifically designated in the figure. The figureshows a β-Ta in a PVD TaN/Ta (device 100) and an α-Ta in ALD TaN/PVD Taor in ALD TaN/PVD TaN/Ta (device 300).

Referring to FIG. 18, shown therein is a device 600 fabricated accordingto various aspects of the present disclosure. Many layers andcompositions of the device 600 are similar to those of the device 300(FIG. 14). Therefore they are labeled with the same reference numeralsfor the purpose of simplicity. However, the device 600 includes a pairof metal barrier layers that is a Ta layer over a TaN layer, which isdifferent from the device 300. In an embodiment, barrier layer 636 is aPVD TaN layer having a thickness in a range from about 10 Å to 20 Å,barrier layer 638 is a PVD Ta layer having a thickness in a range fromabout 50 Å to about 100 Å, and the barrier layer 638 is over the barrierlayer 636. In another embodiment, barrier layer 614 is a PVD TaN layerhaving a thickness in a range from about 10 Å to about 20 Å, barrierlayer 616 is a PVD Ta layer having a thickness in a range from about 50Å to 100 Å, and the barrier layer 616 is over the barrier layer 614. Invarious embodiments, the pair of barrier layers 636/638 may have thesame compositions as or different compositions from the pair of barrierlayers 614/616. For example, in an embodiment, the barrier layers614/616 are PVD TaN/PVD Ta layers while the barrier layers 636 and 638are substantially the same as the barrier layers 336 and 338 (FIG. 14)respectively. In another embodiment, the barrier layers 636/638 are PVDTaN/PVD Ta layers, while the barrier layers 614 and 616 aresubstantially the same as the barrier layers 314 and 316 (FIG. 14)respectively. In yet another embodiment, the barrier layers 614/616 arePVD TaN/PVD Ta layers and the barrier layers 636/638 are also PVDTaN/PVD Ta layers. In various embodiments, the pair of PVD TaN/PVD Talayers of the device 600, such as the 614/616 pair or the 636/638 pair,have N/Ta concentration ratio similar to the device 300 as shown in thegraph 510 (FIG. 16). For example, with respect to the device 600, theN/Ta ratio of the PVD TaN layer is about 2.3 to 2.6, and the N/Ta ratioof the PVD TaN/PVD Ta layers is about 0.6 to 1.0. However, the carbon(C) content of the pair of PVD TaN/PVD Ta layers of the device 600 islower than that of the barrier layers of the device 300. In anembodiment, the carbon (C) content in the PVD TaN/Ta layers of thedevice 600 is lower than about 0.2%.

In various embodiments, the device 600 is also different from the device100 (FIG. 1). For example, the PVD TaN layer of the device 600 (e.g.,the barrier layer 614 and/or the barrier layer 636) is thinner than thePVD TaN layer of the device 100 (e.g., the barrier layers 110, 120and/or 126 in FIG. 1). In various embodiments, the PVD TaN layer of thedevice 600 is thinner than 30 Å, while the PVD TaN layer of the device100 is thicker than 30 Å. Another difference between the device 600 andthe device 100 is the N/Ta ratio in the respective PVD TaN/PVD Tabarrier layers. In various embodiments, the PVD TaN layer of the device600 has a N/Ta ratio about 2.3 to 2.6 (the graph 510 of FIG. 16), whilethe PVD TaN layer of the device 100 has a N/Ta ratio about 0.3 to 0.6(the graph 500 of FIG. 16).

Still referring to FIG. 18, in an embodiment of the device 600, thefirst trench 312 and the second trench 334 each have a CD (e.g., width)ranging from about 0.036 micron (μm) to about 1.0 μm, while the via 332has a CD (e.g., diameter) ranging from about 0.025 μm to about 0.040 μm.In another embodiment of the device 600, the first trench 312 and thesecond trench 334 each have a CD (e.g., width) ranging from about 0.045μm to about 1.0 μm, while the via 332 has a CD (e.g., diameter) rangingfrom about 0.040 μm to about 0.055 μm. In yet another embodiment of thedevice 600, the first trench 312 and the second trench 334 each have aCD (e.g., width) ranging from about 0.064 μm to about 1.0 μm, while thevia 332 has a CD (e.g., diameter) ranging from about 0.055 μm to about0.070 μm.

The device 600 may be fabricated with the method 200 (FIG. 2) inaccordance with some embodiments. In an embodiment, the method 200 formsthe barrier layers 614 and 616 as a pair of PVD TaN and PVD Ta layers inthe step 210. To further this embodiment, the step 210 deposits thebarrier layer 614 on the bottom and the side walls of the first trench312 as shown in FIG. 6 using a first PVD process that includes plasmasputtering a Ta target with a controlled N₂ flow. In the first PVDprocess, the N₂ flow is controlled to be from about 20 Standard CubicCentimeters per Minute (sccm) to about 40 sccm. In an embodiment, the N₂flow is about 30 sccm. In another embodiment, the N₂ flow is about 36sccm. In yet another embodiment, the N₂ flow is from about 30 sccm toabout 40 sccm. In various embodiments, the first PVD process furtherincludes an Ar flow ranging from about 4 sccm to about 50 sccm, a DCpower ranging from about 3 KW to about 15 KW, and an AC power rangingfrom about 75 W to about 250 W. In various embodiments, the thickness ofthe PVD TaN layer 614 is controlled to be about 10 Å to 20 Å. Due to thehigh N₂ flow in combination with the other operation conditions (such asthe Ar flow, DC power, and AC power), the PVD TaN layer 614 attains ahigh N to Ta ratio ranging from about 2.3 to about 2.6. The step 210further includes depositing the barrier layer 616 on the barrier layer614 using a second PVD process. The second PVD process includes plasmasputtering a Ta target without a N2 flow. In various embodiments, thethickness of the PVD Ta layer 616 is controlled to be about 50 Å to 100Å. In an embodiment, the method 200 forms the barrier layers 636 and 638as a pair of PVD TaN and PVD Ta layers in the step 224 using similar PVDprocesses discussed above. Due to the high N/Ta ratio in the PVD TaNlayer 636 (or 614), the PVD Ta layer 638 (or 616) attains higher Tapurity than the PVD Ta layer in the device 100 (FIG. 1). Accordingly,the device 600 attains a lower Rc than the device 100. Furthermore,certain characteristics of the device 600 are comparable with or evenbetter than the device 300, as will be discussed below.

FIG. 19 shows an XRD analysis of various embodiments of the device 600.Referring to FIG. 19, a graph 712 shows Ta compositions in a pair of PVDTaN/PVD Ta layers wherein the PVD TaN layer is formed with an N₂ flowabout 27 sccm. Similarly, graphs 714 and 716 show Ta compositions insuch a pair but with different N₂ flows. Specifically, the embodiment inthe graph 714 uses an N₂ flow about 30 sccm and the embodiment in thegraph 716 uses an N₂ flow about 36 sccm. As can be seen from FIG. 19,the embodiment in the graph 712 includes both β-Ta and α-Ta while theembodiments in the graphs 714 and 716 include increased α-Ta componentand decreased β-Ta component. Specifically, the embodiment in the graph716 comprises α-Ta but substantially no β-Ta. Since β-Ta is generallymore resistive than α-Ta, FIG. 19 at least partially explains why a PVDTaN layer formed with a higher N₂ flow contributes to a lower Rc ofvarious embodiments of the device 600.

When designing an integrated circuit interconnect, such as the devices100, 300, and 600, resistance of the interconnect is of importantconcern. For example, propagation delay t through an interconnect isgenerally expressed as t=RC where R is the resistance of theinterconnect and C is the capacitive load of the interconnect.Therefore, a lower resistance generally contributes to a lowerpropagation delay, hence faster switching speed. Resistance of aninterconnect includes a sheet resistance (Rs) component and a contactresistance (Rc) component. To compare the resistance of the devices 300and 600, both the Rs and Rc components are respectively compared. Tofurther this purpose, an embodiment of the device 300 and twoembodiments of the device 600 are compared through simulations andexperiments, wherein all three embodiments use a layer-5 Cu-containingmetal line with a width 0.045 μm. The embodiment of the device 300 usesa PVD Ta layer (e.g., the barrier layer 338) over an ALD TaN layer(e.g., the barrier layer 336) as metal barrier layers in the via 332.The first embodiment of the device 600 uses a PVD Ta layer (e.g., thebarrier layer 638) over a PVD TaN layer (e.g., the barrier layer 636) asmetal barrier layers in the via 332 where the PVD TaN layer is formedwith an N₂ flow about 30 sccm. The second embodiment of the device 600uses a PVD Ta layer (e.g., the barrier layer 638) over a PVD TaN layer(e.g., the barrier layer 636) as metal barrier layers in the via 332where the PVD TaN layer is formed with an N₂ flow about 36 sccm. FIG. 20compares the Rs of the corresponding metal lines of the threeembodiments. FIGS. 21 and 22 compare the Rc of the three embodiments.

Referring to FIG. 20, a graph 722 shows statistics about the Rs of theembodiment of the device 300. A graph 724 shows statistics about the Rsof the first embodiment of the device 600. Substantially overlapping thegraph 724 is a graph 726 showing statistics about the Rs of the secondembodiment of the device 600. As can be seen from FIG. 20, the Rs of thethree embodiments are about the same.

Referring to FIGS. 21 and 22, graphs 732 and 742 show statistics aboutthe Rc of the embodiment of the device 300, graphs 734 and 744 showstatistics about the Rc of the first embodiment of the device 600, andgraphs 736 and 746 show statistics about the Rc of the second embodimentof the device 600. In each of the graphs, about 484 samples are used.Referring to FIG. 21, the average and median Rc in the graph 732 arelower than those in the graphs 734 and 736. However, the Rc standarddeviation (σ) in the graphs 734 and 736 are smaller than that in thegraph 732, which contributes to more predictable interconnect resistancein the device 600. With respect to the two embodiments of the device 600depicted in the graphs 734 and 736, the Rc standard deviation (σ) isless than about 0.4 Ohms (Ω). FIG. 22 shows the same information as inFIG. 21, but from a different perspective. Furthermore, compared withsome embodiments of the device 100 (the group 402 in FIG. 15), the twoembodiments of the device 600 demonstrate lower Rc generally, similar tothe group 404 in FIG. 15 where the contact resistance (Rc) of the trench312 to the trench 334 ranges from about 6 to about 11Ω while a criticaldimension (CD) of the trenches ranges from about 0.05 to about 0.5micrometer (μm).

The measurements and data shown above are for example purposes only, andare derived with respect to some, but not all, of the embodiments in thepresent disclosure. Accordingly, the present invention should not belimited by these measurements and data, apart from what is explicitlyset forth in the claims.

Thus, the present disclosure describes a structure for an integratedcircuit. The structure includes a substrate, a cap layer deposited onthe substrate, a dielectric layer deposited on the cap layer, and atrench embedded in the dielectric layer. The trench includes an atomiclayer deposition (ALD) TaN or a chemical vapor deposition (CVD) TaNdeposited on a side wall of the trench in which a N/Ta ratio of the ALDTaN or the CVD TaN ranges from about 2.3-2.6, a physical vapordeposition (PVD) Ta or a combination of the PVD Ta and a PVD TaNdeposited on the ALD TaN or CVD TaN in which a N/Ta ratio of the PVD TaNranges from about 0.3 to 0.6 and a N/Ta ratio of the PVD Ta is nearzero, and a Cu deposited on the PVD Ta or the combination of the PVD Taand the PVD TaN deposited on the ALD TaN or the CVD TaN in which a N/Taratio of PVD Ta or the combination of the PVD Ta and the PVD TaN and theALD TaN or the CVD TaN ranges from about 0.6 to 1.0. The structurefurther includes a via integrated into the trench at bottom of thefilled trench. The via reaches to the cap layer. A thickness of the ALDTaN ranges from about 5 to 10 angstrom (Å). A Ta of PVD Ta or the PVDTaN changes from β-Ta to α-Ta. The dielectric layer includes a low-kmaterial with a dielectric constant k ranges from about 2.6 to 2.65. Thedielectric layer further includes Si, C, O and H. A carbon (C)concentration in the ALD TaN and the PVD Ta or the PVD Ta and the PVDTaN deposited on the ALD TaN ranges from about 0.2 to 1 percent (%). Acarbon (C) concentration in the PVD Ta or PVD TaN is less than about0.2%.

In some embodiment, a structure for an integrated circuit is described.The structure includes a substrate, a first cap layer deposited on thesubstrate, a first dielectric layer deposited on the cap layer, a firsttrench embedded in the first dielectric layer, a second cap layerdeposited on the first dielectric layer, a second dielectric layerdeposited on the first dielectric layer, a second trench embedded in thesecond dielectric layer, a via located between the first trench and thesecond trench and integrated into the first trench at top of the filledfirst trench and into the second trench at bottom of the second trench.The first trench or the second trench includes an atomic layerdeposition (ALD) TaN or a chemical vapor deposition (CVD) TaN depositedon bottom and side wall of the first trench, wherein a N/Ta ratio of theALD TaN or the CVD TaN ranges from about 2.3-2.6, a physical vapordeposition (PVD) Ta or a combination of the PVD Ta and a PVD TaNdeposited on the ALD TaN or CVD TaN, wherein a N/Ta ratio of the PVD TaNranges from about 0.3 to 0.6 and a N/Ta ratio of the PVD Ta is nearzero, and a Cu deposited on the PVD Ta or the combination of the PVD Taand the PVD TaN deposited on the ALD TaN or the CVD TaN, where in a N/Taratio of PVD Ta or the combination of the PVD Ta and the PVD TaN and theALD TaN or the CVD TaN ranges from about 0.6 to 1.0.

The present disclosure also describes a method of for fabricating anintegrated circuit. The method includes depositing a cap layer on asubstrate, depositing a dielectric layer on the cap layer, depositing ahard mask layer on the dielectric layer, forming a trench in the firstdielectric layer, and filling the trench. Filling the trench includesdepositing a first barrier layer on bottom and side walls of the trench,depositing a second barrier layer on the first barrier layer, anddepositing a metal on the second barrier layer. The method furtherincludes using a chemical mechanical polishing (CMP) to remove the hardmask layer. Depositing the first barrier layer includes depositing atantalum nitride (TaN) layer with a thickness ranges from about 5 to 10angstrom (Å) using an atomic layer deposition (ALD) process or achemical vapor deposition process (CVD). Depositing the second barrierlayer includes depositing a Ta layer with a thickness ranges from about50 to 100 Å on the first barrier layer using a physical vapor deposition(PVD) process. Depositing the second barrier layer further includesdepositing a TaN layer using a PVD process. Depositing the metalincludes depositing copper (Cu). Depositing the metal further includesdepositing a Cu seed layer.

In one exemplary aspect, the present disclosure is directed to astructure for an integrated circuit. The structure includes a substrate;a cap layer deposited on the substrate; a dielectric layer deposited onthe cap layer; and a trench embedded in the dielectric layer. The trenchincludes a TaN layer formed on a side wall of the trench, wherein theTaN layer has a greater concentration of nitrogen than tantalum; a Talayer formed over the TaN layer; and a Cu-containing layer formed overthe Ta layer. An overall carbon (C) concentration of the TaN layer andthe Ta layer is lower than about 0.2 percent (%).

In another exemplary aspect, the present disclosure is directed to astructure for an integrated circuit. The structure includes a substrate;a first cap layer formed over the substrate; a first dielectric layerformed over the first cap layer; a first trench embedded in the firstdielectric layer. The first trench includes a first TaN layer depositedon bottom and sidewalls of the first trench, wherein the first TaN layerhas a greater concentration of nitrogen than tantalum; a first Ta layerdeposited over the first TaN layer; and a first Cu-containing layerformed over the first Ta layer. The structure further includes a secondcap layer formed over the first dielectric layer; a second dielectriclayer formed over the first dielectric layer; a second trench embeddedin the second dielectric layer. The second trench includes a second TaNlayer deposited on bottom and sidewalls of the second trench, whereinthe second TaN layer has a greater concentration of nitrogen thantantalum; a second Ta layer deposited over the second TaN layer; and asecond Cu-containing layer formed over the second Ta layer. Thestructure further includes a via located between the first trench andthe second trench, wherein the via is integrated into the first trenchat a top portion of the first trench and integrated into the secondtrench at a bottom portion of the second trench.

In yet another exemplary aspect, the present disclosure is directed to amethod of fabricating an integrated circuit. The method includesdepositing a cap layer on a substrate; depositing a dielectric layer onthe cap layer; forming a trench in the dielectric layer; and filling thetrench. The step of filling the trench includes depositing a firstbarrier layer on bottom and sidewalls of the trench using physical vapordeposition (PVD) of TaN with an N₂ flow at least 20 Standard CubicCentimeters per Minute (sccm); depositing a second barrier layer on thefirst barrier layer using PVD of Ta; and depositing a metal layer overthe second barrier layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A structure for an integrated circuit, thestructure comprising: a substrate; a cap layer deposited on thesubstrate; a dielectric layer deposited on the cap layer; and a trenchembedded in the dielectric layer, wherein the trench includes: a TaNlayer formed on a side wall of the trench, wherein the TaN layer has agreater concentration of nitrogen than tantalum; a Ta layer formed overthe TaN layer; and a Cu-containing layer formed over the Ta layer,wherein an overall carbon (C) concentration of the TaN layer and the Talayer is lower than about 0.2 percent (%).
 2. The structure of claim 1,wherein an overall N/Ta ratio of the TaN layer and the Ta layer rangesfrom about 0.6 to about 1.0.
 3. The structure of claim 1, wherein a N/Taratio of the TaN layer ranges from about 2.3 to about 2.6.
 4. Thestructure of claim 1, further comprising a via integrated into thetrench at a bottom portion of the trench, wherein the via reaches to thecap layer.
 5. The structure of claim 4, wherein the trench has a CDabout 0.045 μm and a contact resistance (Rc) of the structure has astandard deviation (σ) less than about 0.4 Ohms (Ω).
 6. The structure ofclaim 1, wherein a thickness of the TaN layer ranges from about 10 toabout 20 angstrom (Å).
 7. The structure of claim 1, wherein a thicknessof the Ta layer ranges from about 50 to about 100 angstrom (Å).
 8. Thestructure of claim 1, wherein the TaN layer and the Ta layer compriseα-Ta but substantially no β-Ta.
 9. The structure of claim 1, wherein theTaN layer and the Ta layer comprise both α-Ta and β-Ta.
 10. A structurefor an integrated circuit, the structure comprising: a substrate; afirst cap layer formed over the substrate; a first dielectric layerformed over the first cap layer; a first trench embedded in the firstdielectric layer, wherein the first trench includes: a first TaN layerdeposited on bottom and sidewalls of the first trench, wherein the firstTaN layer has a greater concentration of nitrogen than tantalum; a firstTa layer deposited over the first TaN layer; and a first Cu-containinglayer formed over the first Ta layer; a second cap layer formed over thefirst dielectric layer; a second dielectric layer formed over the firstdielectric layer; a second trench embedded in the second dielectriclayer, wherein the second trench includes: a second TaN layer depositedon bottom and sidewalls of the second trench, wherein the second TaNlayer has a greater concentration of nitrogen than tantalum; a second Talayer deposited over the second TaN layer; and a second Cu-containinglayer formed over the second Ta layer; and a via located between thefirst trench and the second trench, wherein the via is integrated intothe first trench at a top portion of the first trench and integratedinto the second trench at a bottom portion of the second trench.
 11. Thestructure of claim 10, wherein a contact resistance (Rc) of the firsttrench to the second trench has a standard deviation (σ) less than about0.4 Ohms (Ω).
 12. The structure of claim 10, wherein a contactresistance (Rc) of the first trench to the second trench ranges fromabout 6 to about 11 Ohms (Ω) while a critical dimension (CD) of thefirst trench ranges from about 0.05 to about 0.5 micrometer (μm). 13.The structure of claim 10, wherein a CD of the via ranges from about0.025 to about 0.040 μm while a CD of the first trench or the secondtrench ranges from about 0.036 μm to about 1.0 μm.
 14. The structure ofclaim 10, wherein a CD of the via ranges from about 0.040 to about 0.055μm while a CD of the first trench or the second trench ranges from about0.045 μm to about 1.0 μm.
 15. The structure of claim 10, wherein a CD ofthe via ranges from about 0.055 to about 0.070 μm while a CD of thefirst trench or the second trench ranges from about 0.064 μm to about1.0 μm.
 16. A method of fabricating an integrated circuit, the methodcomprising: depositing a cap layer on a substrate; depositing adielectric layer on the cap layer; forming a trench in the dielectriclayer; and filling the trench, wherein filling the trench includes:depositing a first barrier layer on bottom and sidewalls of the trenchusing physical vapor deposition (PVD) of TaN with an N₂ flow at least 20Standard Cubic Centimeters per Minute (sccm); depositing a secondbarrier layer on the first barrier layer using PVD of Ta; and depositinga metal layer over the second barrier layer.
 17. The method of claim 16,wherein depositing the first barrier layer includes plasma sputtering aTa target with an N₂ flow ranging from about 20 sccm to about 40 sccm.18. The method of claim 17, wherein depositing the first barrier layerfurther includes an Ar flow ranging from about 4 sccm to about 50 sccm,a DC power ranging from about 3 KW to about 15 KW, and an AC powerranging from about 75 W to about 250 W.
 19. The method of claim 16,wherein the first barrier layer is deposited to have a thickness rangingfrom about 10 to about 20 angstrom (Å).
 20. The method of claim 16,wherein the second barrier layer is deposited to have a thicknessranging from about 50 to about 100 Å.